1. Field of the Invention
The present invention relates to Mobile IP network technology. More particularly, the present invention relates to authenticating the identity of a node during proxy registration performed on behalf of the node.
2. Description of the Related Art
Mobile IP is a protocol which allows laptop computers or other mobile computer units (referred to as “Mobile Nodes” herein) to roam between various sub-networks at various locations—while maintaining internet and/or WAN connectivity. Without Mobile IP or related protocol, a Mobile Node would be unable to stay connected while roaming through various sub-networks. This is because the IP address required for any node to communicate over the internet is location specific. Each IP address has a field that specifies the particular sub-network on which the node resides. If a user desires to take a computer which is normally attached to one node and roam with it so that it passes through different sub-networks, it cannot use its home base IP address. As a result, a business person traveling across the country cannot merely roam with his or her computer across geographically disparate network segments or wireless nodes while remaining connected over the internet. This is not an acceptable state-of-affairs in the age of portable computational devices.
To address this problem, the Mobile IP protocol has been developed and implemented. An implementation of Mobile IP is described in RFC 2002 of the Network Working Group, C. Perkins, Ed., October 1996. Mobile IP is also described in the text “Mobile IP Unplugged” by J. Solomon, Prentice Hall. Both of these references are incorporated herein by reference in their entireties and for all purposes.
The Mobile IP process and environment are illustrated in FIG. 1. As shown there, a Mobile IP environment 2 includes the internet (or a WAN) 4 over which a Mobile Node 6 can communicate remotely via mediation by a Home Agent 8 and a Foreign Agent 10. Typically, the Home Agent and Foreign Agent are routers or other network connection devices performing appropriate Mobile IP functions as implemented by software, hardware, and/or firmware. A particular Mobile Node (e.g., a laptop computer) plugged into its home network segment connects with the internet. When the Mobile Node roams, it communicates via the internet through an available Foreign Agent. Presumably, there are many Foreign Agents available at geographically disparate locations to allow wide spread internet connection via the Mobile IP protocol. Note that it is also possible for the Mobile Node to register directly with its Home Agent.
As shown in FIG. 1, Mobile Node 6 normally resides on (or is “based at”) a network segment 12 which allows its network entities to communicate over the internet 4. Note that Home Agent 8 need not directly connect to the internet. For example, as shown in FIG. 1, it may be connected through another router (a router R1 in this case). Router R1 may, in turn, connect one or more other routers (e.g., a router R3) with the internet.
Now, suppose that Mobile Node 6 is removed from its home base network segment 12 and roams to a remote network segment 14. Network segment 14 may include various other nodes such as a PC 16. The nodes on network segment 14 communicate with the internet through a router which doubles as Foreign Agent 10. Mobile Node 6 may identify Foreign Agent 10 through various solicitations and advertisements which form part of the Mobile IP protocol. When Mobile Node 6 engages with network segment 14, Foreign Agent 10 relays a registration request to Home Agent 8 (as indicated by the dotted line “Registration”). The Home and Foreign Agents may then negotiate the conditions of the Mobile Node's attachment to Foreign Agent 10. For example, the attachment may be limited to a period of time, such as two hours. When the negotiation is successfully completed, Home Agent 8 updates an internal “mobility binding table” which specifies the care-of address (e.g., a collocated care-of address or the Foreign Agent's IP address) in association with the identity of Mobile Node 6. Further, the Foreign Agent 10 updates an internal “visitor table” which specifies the Mobile Node address, Home Agent address, etc. In effect, the Mobile Node's home base IP address (associated with segment 12) has been shifted to the Foreign Agent's IP address (associated with segment 14).
Now, suppose that Mobile Node 6 wishes to send a message to a corresponding node 18 from its new location. An output message from the Mobile Node is then packetized and forwarded through Foreign Agent 10 over the internet 4 and to corresponding node 18 (as indicated by the dotted line “packet from MN”) according to a standard internet protocol. If corresponding node 18 wishes to send a message to Mobile Node—whether in reply to a message from the Mobile Node or for any other reason—it addresses that message to the IP address of Mobile Node 6 on sub-network 12. The packets of that message are then forwarded over the internet 4 and to router R1 and ultimately to Home Agent 8 as indicated by the dotted line (“packet to MN(1)”). From its mobility binding table, Home Agent 8 recognizes that Mobile Node 6 is no longer attached to network segment 12. It then encapsulates the packets from corresponding node 18 (which are addressed to Mobile Node 6 on network segment 12) according to a Mobile IP protocol and forwards these encapsulated packets to a “care of” address for Mobile Node 6 as shown by the dotted line (“packet to MN(2)”). The care-of address may be, for example, the IP address of Foreign Agent 10. Foreign Agent 10 then strips the encapsulation and forwards the message to Mobile Node 6 on sub-network 14. The packet forwarding mechanism implemented by the Home and Foreign Agents is often referred to as “tunneling.”
It is often desirable to assign a unique IP address to each user or device within a network. Moreover various protocols enable automatic assignment of IP addresses within a particular network. For instance, in accordance with the Dynamic Host Configuration Protocol (DHCP), network administrators may manage a network centrally and automate the assignment of Internet Protocol (IP) addresses in an organization's network. More particularly, using the Internet's set of protocols (TCP/IP), each device that is capable of connecting to the Internet needs a unique IP address. When an organization sets up its computer users with a connection to the Internet, an IP address must be assigned to each machine. Without DHCP, the IP address must be entered manually at each computer and, if computers move to another location in another part of the network, a new IP address must be entered. DHCP allows a network administrator to supervise and distribute IP addresses from a central point and automatically sends a new IP address when a computer is plugged into a different location within the network.
DHCP uses the concept of a “lease” or amount of time that a given IP address will be valid for a computer. The lease time can vary depending on how long a user is likely to require the Internet connection at a particular location. DHCP is particularly useful in education and other environments where users change frequently. Using very short leases, DHCP can dynamically reconfigure networks in which there are more computers than there are available IP addresses. Thus, DHCP supports static addresses for computers containing Web servers that need a permanent IP address.
Although DHCP functions in a static environment, the assignment of a new IP address each time a computer changes its location within a network is far from ideal within a mobile environment. More particularly, when a mobile node roams to a new location within a network, it would be desirable for the node to maintain its home address. However, provisions have not been made for a node that wishes to maintain a single IP address when it changes its location within a network using DHCP. Moreover, a node that is not mobile enabled cannot currently change its location within a network using DHCP and still maintain its assigned IP address.
It is possible to provide Internet services via a wireless link for mobile users who attach to a network via a connection such as a DHCP connection, even where the node does not support Mobile IP. Specifically, a proxy device may implement Mobile IP on behalf of a node that does not support Mobile IP functionality. One such proxy device is the access point (AP). An Access Point (AP) may be defined as the center point in an all-wireless network or serves as a connection point between a wired and a wireless network. Multiple APs can be placed throughout a facility to give users with WLAN adapters the ability to roam freely throughout an extended area while maintaining uninterrupted access to all network resources.
Patent application Ser. No. 10/080,995, entitled “METHODS AND APPARATUS FOR SUPPORTING PROXY MOBILE IP REGISTRATION IN A WIRELESS LOCAL AREA NETWORK,” discloses a system for communicating subnet addresses of gateways (e.g., Home Agents) that support APs in the network. When an AP receives a data packet, the AP may compare the data packet (e.g., source address) with the AP information for one or more APs to determine whether to send a registration request on behalf of the node. More particularly, the AP determines from the source address whether the node is located on a subnet identical to a subnet of the AP. If the node is located on the subnet of the AP, no Mobile IP service is required on behalf of the node. However, when it is determined from the source address that the node is not located on the subnet identical to the subnet of the Access Point, the AP composes and sends a mobile IP registration request on behalf of the node. For instance, the mobile IP registration request may be composed using the gateway associated with the “home” AP (e.g., having a matching subnet) as the node's Home Agent.
Proxy Mobile IP allows clients to move between networks while maintaining sessions. This is accomplished through Mobile IP control messages such as those disclosed in application Ser. No. 10/080,995, entitled “METHODS AND APPARATUS FOR SUPPORTING PROXY MOBILE IP REGISTRATION IN A WIRELESS LOCAL AREA NETWORK,” by inventors Wang et al, filed on Feb. 20, 2002. In this manner, even clients that do not support Mobile IP may move between networks while maintaining sessions.
As shown in FIG. 2, proxy Mobile IP is supported by multiple Access Points within a wireless Local Area Network (WLAN). In this example, two Access Points 202 and 204 support proxy Mobile IP for sub-network A. In this example, a DHCP server assigns an IP address on sub-network A to the node 205. One of the Access Points 202 and 204 detects whether the IP address of the node 205 is on a different sub-network. Since the IP address of the node 205 is on the same sub-network as the Access Points 202 and 204, proxy registration is not required since the node 205 is in its home network.
Alternatively, if the node 205 were on a different sub-network, a registration request would be composed on behalf of the client 205 and sent to the Foreign Agent. The registration request is then processed by the Foreign Agent, shown here as router 206, and subsequently by the client's Home Agent. Upon completion of registration of the node 205 with its Home Agent, packets addressed to the node 205 are then tunneled to node 205 by its Home Agent via the Foreign Agent and Access Point.
When the node 205 subsequently roams beyond the layer 3 boundary from sub-network A to sub-network B, one of the two Access Points 208 and 210 supporting proxy Mobile IP for sub-network B composes a registration request on behalf of the client 205 once it is determined that the IP address of the node 205 is on a different sub-network. The registration request is then processed by the Foreign Agent, shown here as router 212, and forwarded to the client's Home Agent. Upon completion of registration of the node 205 with its Home Agent, packets addressed to the node 205 are then tunneled to the node 205 by the node's Home Agent via the Foreign Agent and Access Point.
While proxy Mobile IP is advantageous since it allows non-Mobile IP enabled nodes to move while maintaining a session, this method is susceptible to route poisoning and Denial of Service (DoS) attacks. Specifically, another client may send packets with various source IP addresses and MAC addresses. When this second client sends a packet with another client's IP address, the network would then direct traffic to the IP address at the location of the second client because the Access Point would assume that the first client has moved.
In view of the above, it would be desirable if an authentication mechanism could be implemented to authenticate the identity of a client for which proxy Mobile IP registration is being performed.